Light-emitting devices with reflective elements

ABSTRACT

A variety of light-emitting devices are disclosed that are configured to output light provided by a light-emitting element (LEE). In general, embodiments of the light-emitting devices feature two or more light-emitting elements, a scattering element that is spaced apart from the light-emitting elements, an extractor element coupled to the scattering element, and a reflective element that is configured and arranged to reflect light emitted from the light-emitting elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/427,980, filed Mar. 12, 2015, which is a U.S. National Stage ofInternational Application No. PCT/US2013/059544, filed Sep. 12, 2013,which claims benefit under 35 U.S.C. § 119(e)(1) of U.S. ProvisionalApplication No. 61/700,724, filed on Sep. 13, 2012, the entire contentsof which are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to light-emitting devices that include asolid-state based optical system with reflective elements to generatevarious illumination patterns.

BACKGROUND

Historically, many lighting system luminaires have relied upon a singlelight source and single primary reflector and in some implementations, asingle final primary diffuser or “window” that surrounds the lightsource and creates some type of illumination pattern, such as spot lightor area light depending upon the photometric needs in a givenapplication. The light source was generally a nominally 4 pi steradianemitter from either a filament or an electric discharge arc contained inone, or more, volumetric enclosures (e.g., light bulbs.) Given the lackof control over the spatial emission pattern and fixed spectral contentinherent in the underlying technologies, the luminaire designer hasusually relied upon the creation of a fairly large proximate opticalsystem around the light source to achieve a desired, relativelyinvariant photometric distribution. This single light source to onefunction paradigm has prevailed in the lighting industry for well over acentury.

With the advent of high efficiency light-emitting diode (LED) sources,as known in the art, it is possible to obtain large light flux packagesincluding LED die material (e.g., about 1 mm²) along with an appropriatewavelength converting material (e.g., phosphor) placed in proximity tothe die to create a composite light spectrum that is close to thePlanckian locus. As commonly known in the art, the Planckian locus isalso referred to as the black body locus, which mathematically refers tothe set of points that characterize light emitted by a black bodyradiator as a function of the temperature of the black body in aparticular chromaticity coordinate space. These packages are now showingefficacies in the range of 150 lumens/watt such that, for example, a 1watt device can be capable of producing 150 lumens of light or about¼^(th) of the flux of a standard 60 watt incandescent lamp. If theseindividual sources are differentiated and/or operated differentiallythen it is possible to piecewise electronically parse a previouslylarger lighting function into smaller functions in both spectral andspatial respects.

Arrays of powerful compact LED dies or array packages are also availablethat can provide high granularity of control as desired for variousapplications. Some LED dies can have a high current density with highsurface exitance in the shorter wavelength blue, or even ultraviolet,regions of the spectrum such that high optical energy densities can beachieved with less than 0.2 mm² of material, for example. As epitaxialmaterials improve in terms of external quantum efficiencies and energydensities, smaller elements of light can be harnessed in efficientoptical structures.

Therefore, a reduction in the size of the finished optical structure ispossible, and hence the etendue of the light source which can beadvantageously used to create better optically controlled systems usingless material at much lower costs to the final application. The use ofan LED is but one example of a “light emitting element” otherwise knownas an “LEE” which includes Light Emitting Diodes, laser diodes,superluminescent diodes, or organic light emitting diodes and othercompact semiconducting devices as are known in the art.

SUMMARY

Individual LED sources can be electronically and optically isolated in aluminaire design where a variety of lighting functions can beelectronically controlled independently such that the luminaire can betuned spectrally and optically. This can be accomplished by dimmingindividual LEDs independently, or inter-dependently, such that thecomposite light output from all of the LEDs in the system creates aspecific spectral far field illumination distribution that supportsfunctions, such as human biological activation functions, taskorientation, aesthetic functions, performance or efficiency.

In one aspect, a light-emitting device includes a base substrate; two ormore light-emitting elements (LEEs) disposed on the base substrate; afirst optical element having a first surface spaced apart from the LEEsand positioned to receive light from at least one of the LEEs, the firstoptical element having a refractive index n₁ and configured to scatterlight from the LEEs; a second optical element having an exit surface,the second optical element being transparent and having a refractiveindex n₂ that is equal to or larger than n₁, the second optical elementbeing optically coupled with the first optical element and arranged toreceive at least a portion of light through the first optical element;and a reflective element having a first reflective surface and a secondreflective surface, the first reflective surface arranged to reflectlight from one or more first LEEs of the two or more LEEs, the secondreflective surface arranged to reflect light from one or more secondLEEs of the two or more LEEs.

The foregoing and other embodiments can each optionally include one ormore of the following features, alone or in combination. In someembodiments, the second reflective surface opposes first reflectivesurface. In some embodiments, the reflective element extends from thebase substrate toward the first optical element. In some embodiments,the reflective element extends between the base substrate and the firstoptical element, into the second optical element, through the exitsurface, or from the first optical element toward the base substrate. Insome embodiments, the first and second reflective surfaces are arrangedperpendicular to the base substrate. In some embodiments, the first andsecond reflective surfaces are planar.

In some embodiments, the light-emitting device further includes twoadditional reflective elements and the two or more LEEs include at leastthree LEEs, the reflective element and the two additional reflectiveelements separating the one or more first LEEs, the one or more secondLEEs different from the first LEEs, and one or more third LEEs differentfrom the first and second LEEs. In some embodiments, the light-emittingdevice further includes three or more additional reflective elements andthe two or more LEEs include at least four LEEs, the reflective elementand the three or more additional reflective elements separatingrespective LEEs of the at least four LEEs.

In some embodiments, power to the one or more first LEEs and the one ormore second LEEs can be controlled independently. In some embodiments,power to each LEE of the two or more LEEs can be controlled separately.In some embodiments, the first optical element can be configured toisotropically scatter light passing therethrough. In some embodiments,the first optical element can include inelastic scattering centersand/or elastic scattering centers.

In some embodiments, the one or more first LEEs can be configured toprovide light having a first spectral power distribution, and the one ormore second LEEs can be configured to provide light having a secondspectral power distribution different from the first spectral powerdistribution. In some embodiments, at least two of the first LEEs havedifferent spectral power distributions and the at least two of the firstLEEs can be independently controlled. In some embodiments, at least twoof the second LEEs have different spectral power distributions and theat least two of the second LEEs can be independently controlled. In someembodiments, the first optical element can be shaped such that at leastsome light scattered from the first optical element via the firstsurface propagates directly back to another location of the firstsurface.

In some embodiments, the base substrate can have a reflective basesurface facing the first optical element. In some embodiments, the basesurface can be planar. In some embodiments, the base surface can includespecular reflective portions. In some embodiments, the base surface caninclude diffuse reflective portions. In some embodiments, the firstoptical element can have a substantially uniform thickness. In someembodiments, the exit surface can be shaped such that an angle ofincidence on the exit surface of the light provided by the first opticalelement that directly impinges on the exit surface is less than acritical angle for total internal reflection. The exit surface can beshaped such that an angle of incidence on the exit surface of light thatdirectly impinges on the exit surface is less than the Brewster angle.

In some embodiments, an axis of symmetry of the first optical elementand an axis of symmetry of the second optical element can be collinear.In some embodiments, the exit surface can have a spherical shape. Insome embodiments, a medium adjacent to the first surface can be a gas.

In another aspect, a light-emitting device includes a base substrate;multiple light-emitting elements (LEEs) disposed on the base substrate;multiple first optical elements, each first optical element of theplurality of first optical elements having a first surface spaced apartfrom the plurality of LEEs, positioned to receive light from one or moreof the plurality of LEEs, and configured to scatter light passingtherethrough; multiple second optical elements, each second opticalelement of the multiple second optical elements having an exit surface,being transparent and optically coupled with a respective first opticalelement, and arranged to receive light therefrom; and one or morereflective elements disposed between LEEs of the multiple LEEs, the oneor more reflective elements having reflective surfaces arranged toreflect portions of light emitted from the plurality of LEEs, andwherein the one or more reflective elements separate adjacent secondoptical elements.

The foregoing and other embodiments can each optionally include one ormore of the following features, alone or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an example of a light-emittingdevice with a reflective element.

FIG. 2A shows an example of a light-emitting device with a reflectiveelement.

FIG. 2B shows an example of two spectral distributions output by alight-emitting device with a reflective element.

FIGS. 2C-2E show other examples of light-emitting devices withreflective elements.

FIGS. 3A-3C show examples of light-emitting devices with reflectiveelements that delineate various zones.

FIG. 4A shows another example of a light-emitting device with areflective element.

FIGS. 4B-4C show light output distributions of a light-emitting devicewith a reflective element.

FIG. 5 shows an example of a light-emitting device with a secondaryoptic.

FIG. 6 shows an example of a light-emitting device with a light-guide.

FIGS. 7A-7B show an example of a light-emitting device with multiplereflective elements.

FIG. 8 shows an example of a light-emitting device with a reflectivemixing structure.

FIG. 9 shows an example of an electronic control module to controlvarious light-emitting elements.

DETAILED DESCRIPTION

Various embodiments are described within the context of an asymmetric(or symmetric) optical light-emitting device to create a highlyefficient, and variably tunable and steerable device that can be usedwith secondary and tertiary optics to enable the creation of new typesof luminaires or light sources that are applicable to a wide range oflighting functions. These luminaires can be passively and activelytailored to the needs of users and various tasks in the illuminatedenvironment. Furthermore, with the inclusion of advanced controls andsensing, these light-emitting devices can dynamically adapt to users andtasks throughout the day or over the lifetime of the system.

FIG. 1 shows a schematic diagram of an example of a light-emittingdevice 100 that includes multiple light-emitting elements (LEEs) 110,112, a scattering element 120 (also referred to as a first opticalelement), an extractor element 130 (also referred to as a second opticalelement), a recovery enclosure 140 (also referred to as cavity) that isformed, at least in part, by the scattering element 120, and areflective element 150. The light-emitting device 100 can efficientlyprovide broadband, homogenized light to an ambient environment across abroad range of angles.

The scattering element 120 has a first surface (also referred to as alight-entry surface) spaced apart from the light-emitting elements 110,112 and positioned to receive the light from the light-emitting elements110, 112. The scattering element 120 includes scattering centersarranged to substantially isotropically scatter the light from thelight-emitting elements 110, 112 and to provide scattered light. Thescattering element 120 can include elastic scattering centers, inelasticscattering centers, or both. In some implementations, the scatteredlight can include elastically scattered pump light and inelasticallyscattered pump light. The elastically scattered pump light includesphotons that have undergone elastic scattering at the scatteringcenters, and the inelastically scattered pump light includes photonsthat have undergone inelastic scattering at the scattering centers.Photon energy, and therefore wavelength, is conserved in elasticscattering. For example, the spectral distribution of photons remainssubstantially unchanged due to elastic scattering. Rayleigh scatteringis an example of elastic scattering. In inelastic scattering, whichincludes Raman scattering, photon energy is shifted. Accordingly,inelastic scattering changes the spectral distribution of photons.

The scattering element 120 can substantially randomize the direction ofpropagation of light received from light-emitting elements 110, 112 byscattering substantially all light entering the scattering element 120,while allowing substantial portions of light to pass through thescattering element 120. The extractor element 130 is formed from atransparent material, such as a transparent glass or a transparentorganic polymer, having an exit surface. The exit surface of theextractor element 130 is generally a curved, transparent surface. Inother words, changes in the scattered light passing through the exitsurface can be described, for example by Snell's law of refraction, asopposed to an opaque or diffuse surface where further scattering oftransmitted light occurs.

The extractor element 130 is in contact with the scattering element 120,such that there is an optical interface between the scattering andextractor elements at the place of contact. Moreover, the extractorelement 130 is arranged so that light scattered through the opticalinterface enters the extractor element 130. Light from the scatteringelement 120 that directly reaches the exit surface of the extractorelement 130 is referred to as forward light. In some implementations,the extractor element 130 has an elongate shape. Such an elongation canbe parallel, oblique or perpendicular, for example, to an optical axisof the light-emitting device. The extractor element 130 can be shaped topartially or fully circumscribe the scattering element 120. Such anextractor element 130 provides one or more hollows or cavities and oneor more openings or holes. Openings and holes form apertures to receivelight from the light-emitting elements 110, 112 and direct the light atthe first surface of the scattering element 120. Accordingly, theextractor element 130 is shaped as a shell, a spherical shape (e.g., ahemisphere or partial sphere,) or other shape with a certain thicknessor thickness profile.

In some embodiments, the scattering element 120 is partially or fullysurrounded by the extractor element 130 and the optical interfaceincludes corresponding portions of the surface of the scatteringelement. In some embodiments, the extractor element 130 and thescattering element 120 are integrally formed. In an example of such anintegral formation, the optical interface is a notional interface drawnbetween regions of a corresponding integrally formed object, such thatthe optical interface substantially includes interfaces formed by thescattering centers. This may be the case, when the scattering element120 includes scattering centers inside a material that is the same asthe material used to form the extractor element 130, for example. Inthis manner, the scattering element 120 can be shaped as a tile, disc,spherical or aspherical shell or dome, tubular, prismatic or otherelongate shell, or other structure to provide a predetermined spatialprofile of conversion properties to achieve a predetermined light-outputprofile including color and/or brightness homogeneity from thescattering element 120.

In some implementations, an integrally formed extractor/scatteringelement includes scattering centers that are uniformly distributedthroughout the integrally formed element. Accordingly, in suchimplementations, the extractor element and the scattering element arethe same optical element.

The recovery enclosure 140 encloses a medium, such as a gas (e.g., air),adjacent the first surface of the scattering element 120. The recoveryenclosure 140 is arranged and configured to recover a portion of thescattered light that propagates through the first surface into themedium. This means that the recovery enclosure 140 redirects at least aportion of the scattered light back towards the scattering element 120so that at least some of this light exits the scattering element 120into the extractor element 130. The design of the recovery enclosure 140can be selected to reduce the amount of scattered light that returns tothe light-emitting elements 110, 112 (where it can be absorbed). Forinstance, the recovery enclosure 140 can be defined by the first surfaceof the scattering element 120 and/or one or more additional opticalcomponents that redirect such back-scattered light and/or via certainconfiguration of the scattering element as described herein. Forexample, the recovery enclosure 140 can be formed, at least in part, bythe first surface of the scattering element 120 and the reflectiveelement 150.

The reflective element 150 transects at least a portion of thelight-emitting device 100 and provides a means to control the degree ofintermixing of light between the sectors of the device that wouldimpact, for example, the blending of light. At least one light emittingelement is placed in each area of the light emitting device that isdefined in part by the reflective element 150 such that the reflectiveelement redirects a portion of light emitted by the respective lightemitting elements. For example, the light emitting element 110 can beplaced proximate to a first surface of the reflective element 150 andthe light emitting element 112 can be placed proximate to a secondsurface of the reflective element 150.

The relative height and/or position of the reflective element controlsthe degree by which light from each light emitting element is mixedprior to, and after being output from the light emitting device 100. Forexample, the near field luminance of the light output can be controlledsuch that it is continuously variable across the light output surface toa virtually discontinuous change at the boundary defined by thereflective element 150. In some implementations, the reflective element150 can be a continuous sheet or have voids for interblending of lightin the lower cavity, for example. In some implementations, thereflective element 150 can have one end coincident with a plane definedby the light emitting elements 110, 112 or start at some distance abovethe plane as may be desired.

In general, the shape, size, and composition of the recovery enclosure140, reflective element 150, scattering element 120, and extractorelement 130 can vary. The characteristics of each component are selectedbased on the characteristics of the other components and the desiredperformance of the light-emitting device 100. This will be apparent fromthe discussion of specific embodiments of light-emitting devicesdescribed below.

While a single light-emitting element can be placed in each area definedin part by the reflective element, embodiments can, in general, includemore than one light-emitting element in one or more of the areas. Thelight-emitting elements can be configured to provide light havingdifferent or similar spectral power distributions during operation. Forexample, the spectral power distribution of light emitted by one or moreof the light-emitting elements (also referred to as pump light) can beblue, and the spectral power distribution of light emitted by one ormore other light-emitting elements can be red. In this example, thescattering element provides mixed light including the red scatteredlight from the red light-emitting element(s) and the yellow convertedlight from the blue light-emitting element(s), such that the mixed lighthas a mixed spectral power distribution (that includes yellow and red).

FIG. 2A shows a light-emitting device 200 with a hollow hemisphericalextractor element 230 that is designed to fit over a base substrate 245.The light-emitting device 200 includes at least two LEEs 210 and 212 (ora single LEE with at least two independently controlled surface emissionregions) that may have different spectral outputs. Bisecting theextractor element 230 is a reflective element 250 that extends from thebase substrate 245 and projects upwards until it meets the inside of theextractor element 230 thereby creating two discrete recovery enclosures240 and 242 inside the structure. The index of refraction inside therecovery enclosure(s) is lower than the index of refraction of thehollow hemispherical dome and in some cases can be air.

Scattering elements 220 and 222 (e.g., light converting material layers)are applied to the inner surface of the hemispherical extractor element230 such that the scattering element 220 and the scattering element 222can have the same or different properties such as composition,diffusion, mean path length, optical density, surface structure,spectral emission/conversion, thickness or any other property that coulddistinguish the output of one half of the hemisphere from the otherhalf, i.e., that differentiates the light emission properties from oneregion to the next.

The scattering elements 220, 222 have input surfaces 215, 217 spacedapart from the light-emitting elements 210, 212, positioned to receivelight emitted from the light-emitting element 210 and 212 respectively.In this example, the recovery enclosure 240 is formed by the inputsurface 215, the reflective element 250, and a portion of the basesubstrate 245. Similarly, the recovery enclosure 242 is formed by theinput surface 217, the reflective element 250, and a portion of the basesubstrate 245.

The scattering elements 220 and 222 are coupled to the extractor element230 to form optical interfaces 225 and 227 respectively, including ordefined by a region of contact between the scattering elements 220, 222and the extractor element 230. The extractor element 230 receives lightfrom the scattering elements 220, 222 through the optical interfaces225, 227. The optical interfaces 225, 227 are opposite their respectiveinput surfaces 215, 217 of the scattering elements 220, 222.

Generally, the extractor element 230 is formed from a transparentmaterial, such as transparent glass or a transparent organic polymer(e.g., silicone, polycarbonate or an acrylate polymer). The extractorelement 230 has a transparent exit surface 235 through which the lightreceived by the extractor element 230 is output.

FIG. 2B illustrates an example of two different spectral combinations.The blue peak 210′ emitted by LEE 210 is illustrated to be slightlydifferent from the blue peak 212′ emitted by the second LEE 212. Whilein some embodiments the spectral distributions of the LEEs can be thesame, in other implementations, the spectral distributions of the LEEscan be different since, for example, the dominant “pump” wavelengthefficiency may be optimized and better matched to the specificscattering elements (e.g., light converting materials) 220 and 222 thathave respective combined response curves 220′ and 222′.

These example spectral responses are for illustration purposes to showhow deliberate matching of blue pump wavelengths from respective LEEsand varying light converting material properties as known in the art cancreate highly differentiated final spectral responses that can beindependently controlled by varying the forward bias current througheach LEE respectively. Other types of variation are also possible,including intensity profiles, temporal variations in phosphor decaytimes, and localized variations in light converting material profilesand others. Furthermore, differential drive methodologies as known inthe art can be employed to also vary some properties of the respectivematerials or create a differential in the time averaged spectral outputof the system. It is also important to note that the selection of LEEscould include non-pump type LEDs such as red emitters and the selectionof the light converting materials above may not possess any wavelengthconverting properties and instead offer direct transmission or a rangeof diffusion or other optical interactions that provide a differentiatedoutput characteristic. Some light converting materials may also exhibitvarious levels of scattering during wavelength conversion.

In another embodiment illustrated in FIG. 2C and FIG. 2D it is shownthat the relative height of the reflective element 250 can be variedsuch that the height of the element can be non-existent (h=0) to aheight that could extend to the outside surface of the extractor element230, or even beyond as may be desired (not illustrated). FIG. 2D showsan example where the reflective element 250 extends to the outsidesurface of the extractor element 230. The reflective element 250transects a portion of the light-emitting device 200 and provides ameans to control the degree of intermixing between the sectors of thedevice that would impact, for example, the blending of light.

The relative height of this element controls the degree by which eachLEE is mixed prior to, and after reaching the inner surface of thestructure. As shown in FIGS. 2C and 2D, the near field luminance at thesurface of the device can be controlled such that it is continuouslyvariable across the surface to a virtually discontinuous change at theboundary defined by the reflective element 250. Furthermore, thereflective element 250 does not need to be a continuous sheet but couldhave voids for interblending of light in the lower recoveryenclosure(s). The reflective element 250 may or may not have one endcoincident with the plane of the base substrate 245 and therefore couldstart at some nominal distance above the plane as may be desired.

FIG. 2C shows an example of a light-emitting device 200 with areflective element 250 placed between light-emitting elements 210 and212 that extends from the base substrate 245 into a recovery enclosure240 defined by the scattering element 220 and a portion of the basesubstrate 245. In this example some of the light emitted by thelight-emitting elements 210 and 212 is mixed in an area above thereflective element 250, before entering the scattering element 220.

FIG. 2D shows an example of a light-emitting device 200 with areflective element placed between light-emitting elements 210 and 212that extends from the base substrate 245 to exit surfaces 235 and 237 ofextractor elements 230 and 232 respectively. In this example, lightemitted by the light-emitting element 210, or reflected by thecorresponding surface of the reflective element 250 is received by theextractor element 230 through the scattering element 220 and outputthrough exit surface 235 of the extractor element 230. Similarly, lightemitted by the light-emitting element 212, or reflected by thecorresponding surface of the reflective element 250 is received by theextractor element 232 through the scattering element 222 and outputthrough exit surface 237 of the extractor element 232. Thus, the lightemitted by the light-emitting element 210 and 212 respectively is notmixed before it is output from the respective exit surfaces 235 and 237.

While FIGS. 2A-2D show examples of light-emitting devices that includeextractor elements, other implementations of light-emitting devices asdescribed herein may not include an extractor element. FIG. 2E shows anexample of a light-emitting device 270 with a scattering element 220through which light is output towards a target area. Light emitted bythe light-emitting elements 210, 212, or reflected by the correspondingsurface of the reflective element 250 is received by the input surface215 and output through the surface 225 of the scattering element 220 asscattered light. While the reflective element 250 as shown in FIG. 2Eextends from the base substrate 245 to the scattering element 220, otherconfigurations of reflective elements are also possible. For example,the reflective element can extend from the base substrate 245, orscattering element 220, into the recovery enclosure 240 and/or extendthrough the scattering element 220 to the surface 225, or past thesurface 225.

FIG. 3A shows a light-emitting device 300 with a reflective element 350that delineates two zones (recovery enclosures) 340, 342. Thelight-emitting device 300 includes LEE 310 that is disposed on a basesubstrate in the zone 340 and LEE 312 that is disposed on the basesubstrate in the zone 342. A portion of light emitted by LEEs 310 and312 is reflected by the reflective element 350 towards correspondingportions 320 and 322 of the scattering element. An extractor element 330is coupled with the portions 320 and 322 of the scattering element andconfigured to output the light received through the scattering element.

While one reflective element is shown in FIG. 3A, a light-emittingdevice can also include multiple reflective elements.

FIG. 3B shows how reflective elements 350, 352, and 354 can bestructured such that they delineate 3 zones (recovery enclosures) 340,342, and 344. Numerous zones, configurations and variations arepossible, and the number and/or types of LEEs included in each zone canalso be modified to create various degrees of controlled surfaceluminance at the outer extremity of the extractor element 330. In thisexample, LEE 310 is disposed in the zone 340, LEE 312 is disposed in thezone 342, and LEE 314 is disposed in the zone 344. A portion of thelight emitted by LEEs 310, 312, and 314 is reflected by correspondingsurfaces of the reflective elements 350, 352, and 354 towards portions320, 322, and 324 of the scattering element. The extractor element 330is coupled with the portions 320, 322, and 324 of the scattering elementand configured to output the light received through the scatteringelement.

FIG. 3C illustrates 4 zones (recovery enclosures) 340, 342, 344, and 346delineating 4 quadrants with two adjacent quadrants populated, forexample, by one type of LEE 310 and the other two adjacent quadrantspopulated by a second type of LEE 312 (in some implementations, eachzone can have different or similar types of LEEs, or any combinationthereof) Furthermore, the optical and physical properties of reflectiveelements 350, 352, 354, and 356 are free to be individually modified ina variety of ways such that the surface luminance and relativeuniformity gradients at the surface of the extractor element 330 arecontrolled in a desirable fashion. These reflective elements may vary inrelative height along their longitudinal direction, they may be specularon one side and diffuse reflecting on the other or varied along theirlongitudinal directions or they may be sloped or turned into curvedsections which may or may not intersect the base substrateperpendicularly.

Independent or dependent control of multiple channels of drive currentto LEEs 310 and LEEs 312 can be combined in many ways to regulate lightoutput of any of these components. When these channels are controlled ina variety of ways it is possible to significantly modify the surfaceluminance of the system electronically. This then can be translatedthrough an optical system to the far field by secondary and tertiaryoptical elements such that the far field illuminance and spectralcontent can be controlled in a manner that optimizes the visual andnon-visual impact of the illumination.

In this example, LEE 310 is disposed in the zone 340, LEE 312 isdisposed in the zone 342, LEE 314 is disposed in the zone 344, and LEE316 is disposed in zone 346. A portion of the light emitted by LEEs 310,312, 314, and 316 is reflected by corresponding surfaces of thereflective elements 350, 352, 354, and 356 towards portions 320, 322,324, and 326 of the scattering element. The extractor element 330 iscoupled with the portions 320, 322, 324, and 326 of the scatteringelement and configured to output the light received through thescattering element.

In another embodiment, recent research in human response to lighting isshowing that humans have evolved such that they are profoundlypsychologically and physiologically influenced by the non-visualcomponent of light. In this case, certain wavelengths of light asencountered in nature are pre-disposed to be collected by specificretinal ganglion cells in the human eye that are located within the eyethat corresponds to certain angular input angles relative to the eye'snormal direction of view to the horizon.

FIG. 4A shows an example of a light-emitting device 200 with areflective element. FIG. 4B schematically shows example component lightoutput distributions associated with two portions of the light-emittingdevice 200. FIG. 4C schematically shows superimposed total light outputdistributions of the light-emitting device 200. The light-emittingdevice 200 creates two different distributions 455 and 465 that radiatein different directions and that could be used to provide for angularlydifferentiated light distributions within an illuminated environment.The spectral content present in 455 and 465 can be different and theirtwo distributions follow the principle of superposition such that theycreate a melded intensity distribution 475 and 485 as shown in FIG. 4C.The left side of the distribution is thus differentiated from the rightside distribution in a fairly smooth transition region 480, depicted bywhere the two line patterns merge, that can be oriented such that theone hemisphere 475 distribution is substantially directed to one side ofa plane that coincides with the central axis and the second hemisphere485 is substantially directed to the other side of the same plane.

The light-emitting device 200 includes a base substrate 245, LEEs 210and 212, scattering elements 220 and 222, extractor element 230, andreflective element 250. LEE 210 is disposed on the base substrate 245 ina recovery enclosure 240 that is formed by a portion of the basesubstrate 245, the scattering element 220, and the reflective element250. LEE 212 is disposed on the base substrate 245 in a recoveryenclosure 242 that is formed by a portion of the base substrate 245, thescattering element 222, and the reflective element 250. The scatteringelement 220 includes a surface 217 that faces the LEE 210 and thescattering element 222 includes a surface 215 that faces the LEE 212.

For example, LEE 210 outputs rays 410, 420, and 430, and LEE 212 outputsrays 440 and 450. Rays 410 and 430 directly impinge on the surface 217of the scattering element 220, and rays 440 and 450 directly impinge onthe surface 215 of the scattering element 222. Ray 430 passes throughthe scattering element 220 into the extractor element and is outputthrough exit surface 235 of the extractor element. Ray 410 isbackscattered into the recovery enclosure 240, redirected by the basesubstrate 245 towards the scattering element 220 and output through theexit surface 235 of the extractor element. Ray 420 impinges on thereflective element 250 and is redirected by the reflective element 250towards the scattering element 220. Ray 450 is backscattered into therecovery enclosure 242 and redirected by the reflective element towardsthe scattering element 222. Rays 410 and 420 are a representativeportion of the distribution 475 and ray 450 is a representative portionof the distribution 485. Rays 430 and 440 are representative portions ofthe transition distribution 480.

The addition of external optics can further transform either side of theradiation pattern into a narrower or wider distribution as may berequired, while observing the preservation of etendue through thesystem. By selecting a preferred spectral distribution for biologicalproperties for either 475 or 485 it can be appreciated that theorientation of the light-emitting device, along with external opticalcontrol surfaces can provide for selective spatial distributions withinthe space that correspond to preferred angles of incidence for humanbiological effectiveness.

FIG. 5 shows how an example of how a distribution in the left part ofthe light-emitting device 500 could be manipulated by a secondary optic590 such that the bundle of rays 570, 570′ emit primarily to the rightfrom the reflector and vice versa for the bundle of rays 580, 580′. If acontrol circuit is combined with this system then it is possible toelectronically manipulate both the spectral content and the coarse farfield photometric distribution of light. The methods for controllinglight are well understood in the art and can include signals from acentral control system or from one or more sensors including occupancysensors, cameras or other devices that are brought to the control inputpoint of the controller. Within the controller, logic circuits andoptional program code can independently or inter-dependently control twoor more external circuits that correspond to light-emitting elements 510and 512 (disposed on a base substrate 545) which will then affect theleft or right spectral content and their relative amplitudes within thelight-emitting device.

A light-emitting device can be coupled with optical mixing structures tocreate a uniform emission of blended light. Such mixing structures canbe used to blend the geometrical and spectral output of different lampsinto light that has a certain chromaticity distribution, fluxdistribution or both chromaticity and flux distribution across the exitface 698. Many different mixing structures can be envisioned, includingcoupling optics that collect the emitted light and introduce it into ahollow or solid light-guide where at least a few aspect ratios ofinternal mixing are encountered before final emission. The notion ofaspect ratio is defined in this case to be the numerical ratio of guidelength and smallest guide cross sectional dimension.

In FIG. 6 this ratio is defined as the ratio of h divided by d. Anexample device 600 includes a coupling optic 690 that surrounds alight-emitting device, such as light-emitting device 200, and collectsand introduces the light into a waveguide 695 where it is guided viatotal internal reflection (TIR) or by specular reflection from sidewalls until it reaches an exit surface 698 where it can be utilized byadditional optical components or allowed to radiate into the space.Under appropriate input and geometric conditions, light rays 685, 685′are mixed such that their overall radiation pattern at 698 is wellhomogenized with low losses along the guide. For typical input insertionangles between 30 and 40 degrees from the axis of the light-guide,aspect ratios greater than 5 will result in homogenization that isusually better than 90% across surface 698.

Adjustments to aspect ratio relative to mean input insertion angles canbe made in the design to achieve the desired level of mixing to suit theillumination requirements. Lower ratios can also be used. Further,microscopic optical structures can be used, or the outer walls of thelight-guide can be shaped, or structures within the guide or at the exitof the guide can provide additional reflection components to improve theresult for desired homogeneity. It is also noted that the utilization ofthe light at the exit surface 698 can be coupled into other opticalstructures that can manipulate the beam pattern, including splitting itinto multiple radiation patterns, for subsequent use within a space.Shorter aspect ratios can also add value by providing varying degrees ofmixing such that inhomogeneity is preserved for later use in downstreamoptical systems.

FIGS. 7A and 7B show another embodiment 700 with a non-linear reflectiveelement 760 that is non-perpendicular to a plane of substrate 745. Herethe reflective element 760 is a shown as roughly a conic section thatcondenses light flux from LEE 712 to a portion 722 of a scatteringelement near the top center of the dome. This can create a localizedsource of luminance 771, 771′, 771″, which could be roughly captured anddirected in one direction by secondary optical elements 790. In thiscase, the optical elements 790 could be directing light downwards from aceiling and constitute the provision of localized task illumination, forexample. The optical elements 790 may be specular and could be curved toaid in capture and re-direction of light flux downwards in a prescribednominal controlled beam pattern.

The illumination 772, 772′ provided by a combination of light fromlight-emitting element 710 and a portion 720 of the scattering elementinhabits the lower spatial angles of the hemisphere and can therefore beused to provide a differentiated spectrum of higher angle light to thespace. Other optical surfaces could be employed in regions or zones tomodify the light distributions into the space as desired.

Optionally, the reflective element 790, or secondary reflectors couldredirect and provide an element of optical control to address glare fora flux output 772, 772′. The embodiment of FIGS. 7A and 7B could beutilized within a ceiling luminaire that has electronically controllablecontributions in both spectral output and spatial zones to the taskillumination and independently to the higher angle fill light.Furthermore, flux output 772, 772′ may be created as a variably tunablebiologically active contributor to the space so that the spectralcontribution to the higher angles varies throughout the day via aprogram that is resident either remotely or locally within a controller.For example, a higher blue content type of light could be directed toradiate more towards the ceiling while lower blue content type of lightcould be reserved for downwards emission towards tasks.

In some implementations, the light output of one or more light-emittingelements of a light-emitting device can be controlled independently. Bycontrolling the electrical current passing through each of the LEEs itis possible to electronically vary the respective spectral compositionssuch that the overall integrated composition of light from the assemblycan be varied, or tuned, between the spectral power distributions. If anoptical structure with diffuse internal surfaces and a correctlyspecified diffuse transmission property is employed with thelight-emitting device then a uniform emission of blended light can becreated. Such structures can, for example, blend the geometrical andspectral output of different lamps into a homogenous surface luminanceat the exit face.

FIG. 8 shows an illumination device 800 with an internally diffusivelyreflective mixing structure 861 with a diffusely transmissive exitwindow material 863 that effectively mixes the emitted light spectralcontributions 870 and 880 of a light-emitting device, such aslight-emitting device 200, internally such that there is a compositeemission of radiation 875, 885 from the apparatus.

FIG. 9 shows an example of an electronic control block 900 that can beconfigured to control light-emitting elements 910 and 912. MultipleLEE's can be included in each leg of control and furthermore, additionalchannels of control could be added to enable additional levels ofcontrol of surface luminance. Controller 950 derives power from a point935 which can be optionally a source of alternating current, or a formof direct current or combinations thereof, and uses control signal 945as an input to control the relative power delivered to thelight-emitting elements 910 and 912 as may be defined within the controlcode or by design.

As discussed herein, independent control of LEEs within a light-emittingdevice can be used to adjust a light output of the light-emitting devicewith respect to the needs and/or activities of a user. Furthermore,independent control of LEEs can be used to balance the light output ofthe light-emitting device over the lifetime of the light-emittingdevice. Properties (e.g., material properties) of solid statelight-emitting devices may change over their lifetime. For example, thewhite point of a white LED can vary as the device ages. Accordingly, insome implementations, light-emitting devices can include intra-devicefeedback that enables a device to self-compensate for aging effects. Insome implementations, a light-emitting device includes one or moresensors that can monitor certain electrical or other system parametersand/or the intensity of light generated by the light-emitting device.The light-emitting device can include feedback electronics (e.g., withinthe base of the device) that modify the potential applied to one or morelight-emitting element(s) in response to variations in the detectedintensity.

The term “light-emitting element” (LEE), also referred to as a lightemitter, is used to define any device that emits radiation in one ormore regions of the electromagnetic spectrum from among the visibleregion, the infrared region and/or the ultraviolet region, whenactivated. Activation of a LEE can be achieved by applying a potentialdifference across components of the LEE or passing a current throughcomponents of the LEE, for example. A light-emitting element can havemonochromatic, quasi-monochromatic, polychromatic or broadband spectralemission characteristics. Examples of light-emitting elements includesemiconductor, organic, polymer/polymeric light-emitting diodes (e.g.,organic light-emitting diodes, OLEDs), other monochromatic,quasi-monochromatic or other light-emitting elements. Furthermore, theterm light-emitting element is used to refer to the specific device thatemits the radiation, for example a LED die, and can equally be used torefer to a combination of the specific device that emits the radiation(e.g., a LED die) together with a housing or package within which thespecific device or devices are placed. Examples of light emittingelements include also lasers and more specifically semiconductor lasers,such as vertical cavity surface emitting lasers (VCSELs) and edgeemitting lasers. Further examples include superluminescent diodes andother superluminescent devices.

As described herein, a scattering element can include elastic scatteringcenters, inelastic scattering centers, or both. In general, inelasticscattering entails emission of light from a scattering center in effectof absorption of light by the scattering center. With respect to theinstant technology, inelastic scattering typically is associated withone visible or ultraviolet (UV) incoming photon and one visible outgoingphoton. Scattering of light by a scattering center can result fromeffects such as light conversion, refraction, and/or other effect and/orcombination thereof. The distribution of a plurality of outgoing photonsthat result from inelastic scattering at a single scattering center canbe isotropic depending on, for example, the ability of the scatteringcenters to perform light conversion. The distribution of a plurality ofoutgoing photons that result from elastic scattering at multiplescattering centers can be isotropic depending on, for example, shapes,arrangements and/or compositions of the scattering centers.

A scattering center can include one or more portions that each scatterlight in one or more ways, for example, by light conversion, refractionor other effect. Scattering centers include discontinuities in thecomposition or structure of matter. In order to achieve a predetermineddegree of randomness in its propagation, light may have to undergomultiple elastic scattering events. As such multiple scattering eventsmay be required to achieve a predetermined randomness in the propagationof the light emitted from a scattering element, for example, when thelight is scattered by interaction with scattering centers that scatterlight merely by refraction. Scattering centers can includelight-converting material (LCM) and/or non-light converting material,for example. As used herein, light conversion via LCM is considered aform of inelastic scattering.

LCM is a material, which absorbs photons according to a first spectraldistribution and emits photons according to a second spectraldistribution. The terms light conversion, wavelength conversion and/orcolor conversion are used interchangeably. Light-converting material isalso referred to as photoluminescent or color-converting material, forexample. As used herein, light-converting materials can includephotoluminescent substances, fluorescent substances, phosphors, quantumdots, semiconductor-based optical converters, or the like.Light-converting materials also can include rare earth elements.

Moreover, while the scattering element is shown in the figures with aconstant thickness (e.g., uniform thickness,) the thickness of thescattering element can also vary. Variations of the thickness of thescattering element may be used to vary scattering or other properties ofthe scattering element or the scattered light provided by the scatteringelement, for example.

Recovery enclosure(s) of light-emitting devices described herein caninclude a medium, such as a gas (e.g., air), adjacent a first surface ofa scattering element having a refractive index n0, and the scatteringelement includes a material having a first refractive index n1, wheren0<n1. Light from the scattering element that reaches the first surfaceis referred to as backward light. Because n0<n1, the first surfaceallows only a fraction of the backward light to escape into thelow-index medium. The transparent material of an extractor elementcoupled with the scattering element has a refractive index n2, wheren0<n2. As such, the amount of transmitted forward light is greater thanthe amount of backward light transmitted into the low index medium, andthe light-emitting device asymmetrically propagates scattered light.

In such a case, depending on the degree of asymmetry between n1/n0 andn2/n1 varying ratios of forward to backward light transmission can beprovided. It is believed that the maximum asymmetry in forward tobackward light transmission is reached if n2 is equal to n1 (no mismatchfor forward transmission) and n0<<n1 (large mismatch for backwardtransmission). Light emitting devices that feature asymmetric opticalinterfaces (i.e., different refractive index mismatches) on opposingsides of the scattering element are referred to as asymmetric scatteringlight valves (ASLV), or ASLV light-emitting devices.

The exit surface of the extractor element is a transparent surface onwhich the scattered light that directly impinges on the exit surfaceexperiences little or no total internal reflection (TIR). In thismanner, the exit surface transmits a large portion of light impingingthereon that directly propagates thereto from the scattering element andpropagates in at least certain planes and outputs it into the ambient ofthe extractor element on first pass. The light output through the exitsurface can be used for illumination or indication functions provided bylight-emitting devices or for further manipulation by another opticalsystem that works in conjunction with a light-emitting device.

In some embodiments, the exit surface of the extractor element is shapedas a spherical (e.g., hemisphere or partial sphere) or a cylindricaldome or shell with a radius R1 in which the optical interface isdisposed within an area defined by a respective notional sphere orcylinder that is concentric with the exit surface and has a radiusR_(OW)=R1/n2, wherein n2 is the refractive index of the extractorelement. Such a configuration is referred to as Weierstrass geometry orWeierstrass configuration. It is noted that a spherical Weierstrassgeometry can avoid TIR for rays passing through the area circumscribedby a corresponding notional R1/n2 sphere irrespective of the plane ofpropagation. A cylindrical Weierstrass geometry can exhibit TIR forlight that propagates in planes that intersect the respective cylinderaxis at shallow angles even if the light passes through an areacircumscribed by a corresponding notional R_(OW)=R1/n2 cylinder.

It is noted that other light-emitting devices described in thisspecification have exit surfaces with other shapes and/or othergeometrical relations with respect to the optical interface. Forinstance, a non-spherical or non-cylindrical exit surface of theextractor element can be employed to refract light and aid in shaping anoutput intensity distribution in ways different from those provided by aspherical or cylindrical exit surface. The definition of the Weierstrassgeometry can be extended to include exit surfaces with non-circularsections by requiring that the optical interface falls within cones,also referred to as acceptance cones, subtended from points p of theexit surface whose axes correspond to respective surface normals at thepoints p and which have an apex of 2*Arcsin(k/n), wherein k is apositive number smaller than n.

It is noted that the exit surface needs to be configured such that theplurality of all noted cones circumscribe a space with a non-zerovolume. It is further noted that k is assumed to refer to a parameterthat determines the amount of TIR at an uncoated exit surface thatseparates an optically dense medium, having n>1, on one side of the exitsurface making up the extractor element from a typical gas such as airwith n˜1.00 at standard temperature and pressure conditions, on theopposite side of the exit surface.

Depending on the embodiment, k can be slightly larger than 1 but ispreferably less than 1. If k>1, some TIR may occur at the exit surfaceinside the extractor element. In some embodiments, this results in theoptical interface being at least R(p)*(1−k/n) away from the exit surfacein a direction normal to the exit surface at a point p thereof. Here,R(p) is the local radius of curvature of the exit surface at the pointp, and n is the refractive index of the extractor element. For aspherical or cylindrical exit surface with k=1, the boundariescircumscribed by the noted cones correspond with a spherical orcylindrical Weierstrass geometry, respectively. Some embodiments areconfigured to allow for some TIR by choosing k>1. In such cases, k/n islimited to k/n<0.8, for example.

In summary, a light-emitting device is said to satisfy the Weierstrassconfiguration if a radius R_(O) of the optical interface is less than orequal to R_(O)≤R_(OW)=R1/n2, where R1 and n2 respectively are the radiusand index of refraction of the extractor element. Equivalently, theextractor element of a light-emitting device is said to satisfy theWeierstrass configuration if a radius R₁ of an extractor element, whichhas an index of refraction n2, is equal to or larger thanR₁≥R_(1W)=n2R_(O), where R_(O) is the radius of the optical interface ofthe light-emitting device.

In some embodiments, the exit surface is shaped such that an angle ofincidence on the exit surface of the scattered light that directlyimpinges on the exit surface is less than the Brewster angle. In thiscase, k is not just smaller than 1 to avoid TIR at the exit surface ofthe extractor element for light propagating in at least one plane, but kis made so small that certain Fresnel reflections are additionallyavoided. In such a case, k is chosen to be smaller thann2(1+n2²)^(−1/2). For example, with respect to light propagating inplanes of symmetry of spherical or cylindrical Weierstrass geometries,rays that propagate through an area circumscribed by a concentricnotional sphere or cylinder of radius R0=R1(1+n2²)^(−1/2), will impingeon the exit surface at or below the Brewster angle. More generally,p-polarized light that impinges at a point p of the exit surface fromwithin directions bound by a cone subtended from the point p with apex2*Arctan(1/n) whose axis corresponds with the surface normal at thepoint p will not be reflected at the exit surface. Such a configurationis referred to as Brewster geometry (or Brewster configuration), or morespecifically a Brewster sphere or a Brewster cylinder, for example. Insuch embodiments the distance between the exit surface and the opticalinterface is larger than R1(1−(1+n2²)^(−1/2)).

In summary, a light-emitting device is said to satisfy the Brewsterconfiguration if a radius R₀ of the optical interface is less than orequal to R_(O)≤R_(OB)=R1(1+n2²)^(−1/2), where R₁ and n2 are the radiusand index of refraction of the extractor element. Note that for a givenradius R₁ of the extractor element, an optical interface of thelight-emitting device that satisfies the Brewster condition has amaximum radius R_(OB) that is smaller than a maximum radius R_(OW) of anoptical interface of the light-emitting device that satisfies theWeierstrass condition. Equivalently, the extractor element of index ofrefraction n2 is said to satisfy the Brewster configuration if a radiusR₁ of the extractor element is equal to or larger thanR₁≥R_(1B)=R_(O)(1+n2²)^(+1/2), where R_(O) is the radius of the opticalinterface of the light-emitting device. Note that for a given radiusR_(O) of the optical interface of the light-emitting device, anextractor element that satisfies the Brewster condition has a minimumradius R_(1B) that is larger than a minimum radius R_(1W) of anextractor element that satisfies the Weierstrass condition.

Moreover, a light-emitting device can be fabricated using conventionalextrusion and molding techniques and conventional assembly techniques,as described below in this specification for specific embodiments.Components of the light-emitting device can include one or more organicor inorganic materials, for example acrylic, silicone, polypropylene(PP), polyethylene terephthalate (PET), polycarbonate, polyvinylidenefluoride such as Kynar™ lacquer, acrylic, rubber, polyphenylene sulfide(PPS) such as Ryton™, polysulfone, polyetherimide (PEI),polyetheretherketone (PEEK), polyphenylene oxide (PPO) such as Noryl™,glass, quartz, silicate, adhesive, other polymers organic or inorganicglasses and/or other materials.

A number of embodiments have been described. Other embodiments are inthe following claims.

What is claimed is:
 1. A light-emitting device, comprising: a basesubstrate; a plurality of light-emitting elements (LEEs) disposed on thebase substrate; a plurality of first optical elements, each firstoptical element of the plurality of first optical elements having afirst surface spaced apart from the plurality of LEEs, positioned toreceive light from one or more of the plurality of LEEs, and configuredto scatter light passing therethrough; a plurality of second opticalelements, each second optical element of the plurality of second opticalelements having an exit surface, being transparent and optically coupledwith a respective first optical element, and arranged to receive lighttherefrom; and one or more reflective elements disposed between LEEs ofthe plurality of LEEs, the one or more reflective elements havingreflective surfaces arranged to reflect portions of light emitted fromthe plurality of LEEs, and wherein the one or more reflective elementsseparate adjacent second optical elements.
 2. The light-emitting deviceof claim 1, wherein each of the reflective elements has reflectivesurfaces opposing each other.
 3. The light-emitting device of claim 1,wherein each of the reflective elements extends through exit surfaces ofadjacent second optical elements.
 4. The light-emitting device of claim1, wherein the reflective elements extends from the second opticalelements toward the base substrate.
 5. The light-emitting device ofclaim 1, wherein the reflective surfaces of the reflective elements arearranged perpendicular to the base substrate.
 6. The light-emittingdevice of claim 1, wherein the reflective surfaces of the reflectiveelements are planar.
 7. The light-emitting device of claim 1, whereinpower to one or more LEEs disposed on one side of one of the reflectiveelements and one or more LEEs disposed on opposing side of the one ofthe reflective elements is controlled independently.
 8. Thelight-emitting device of claim 1, wherein power to each LEE of theplurality of LEEs is controlled separately.
 9. The light-emitting deviceof claim 1, wherein each of the first optical elements is configured toisotropically scatter light passing therethrough.
 10. The light-emittingdevice of claim 1, wherein each of the first optical elements comprisesinelastic scattering centers.
 11. The light-emitting device of claim 1,wherein each of the first optical elements comprises elastic scatteringcenters.
 12. The light-emitting device of claim 1, wherein one or moreof the LEEs disposed on one side of one of the reflective elements areconfigured to provide light having a first spectral power distribution,and one or more of the LEEs disposed on opposing side of the one of thereflective elements are configured to provide light having a secondspectral power distribution different from the first spectral powerdistribution.
 13. The light-emitting device of claim 1, wherein at leasttwo of the LEEs disposed on one side of one of the reflective elementshave different spectral power distributions and the at least two of theLEEs are independently controlled.
 14. The light-emitting device ofclaim 13, wherein at least two of the LEEs disposed on opposing side ofone of the reflective elements have different spectral powerdistributions and the at least two of the LEEs are independentlycontrolled.
 15. The light-emitting device of claim 1, wherein the basesubstrate has a reflective base surface facing the first opticalelements.
 16. The light-emitting device of claim 15, wherein the basesurface is planar.
 17. The light-emitting device of claim 15, whereinthe base surface comprises specular reflective portions.
 18. Thelight-emitting device of claim 15, wherein the base surface comprisesdiffuse reflective portions.
 19. The light-emitting device of claim 1,wherein each of the first optical elements has a substantially uniformthickness.
 20. The light-emitting device of claim 1, wherein the exitsurface of each of the second optical elements is shaped such that anangle of incidence on the exit surface of the light provided by acorresponding first optical element that directly impinges on the exitsurface is less than a critical angle for total internal reflection. 21.The light-emitting device of claim 1, wherein an axis of symmetry of theeach first optical element and an axis of symmetry of a correspondingsecond optical element are collinear.
 22. The light-emitting device ofclaim 1, wherein the exit surface of each of the second optical elementshas a spherical shape.
 23. The light-emitting device of claim 1, whereina medium adjacent to the first surfaces is a gas.